Wireless communications systems are now widely used for voice and data communications applications. A variety of different types of devices may be used with a wireless (e.g., cellular) network, including, but not limited to mobile terminals, notebook computers or personal digital assistants (PDAs) with built-in wireless transceivers, and peripheral devices, such as wireless broadband cards, that may be used to provide wireless communications for computers and other electronic device.
Conventional implementations are typically band specific. In particular, even if a carrier or wireless network provider (like a cellular or PCS operator) owns frequency allocations in multiple bands (for example 800 MHz cellular and 1800 MHz PCS), each system typically is designed to operate independently and carry out communication within one band segment, e.g., either the 800 MHz allocation or the 1800 MHz allocation. Multi-band systems have also been designed that can switch between the diverse bands at different times.
Different performance characteristics apply to different frequency bands. In general, all other considerations being equal, higher frequency signals generally provide shorter propagation distances. Lower frequency signals also generally perform better in non line of sight conditions due to their diffraction propagation characteristics.
Other techniques may be used to control signal propagation. For example, in wireless broadband data networks, more bandwidth may be available to users who have the best signal to noise (S/N) margins. As the signal strength falls, these broadband systems may reduce modulation complexity and/or increase the amount of error correction in order to maintain a communication channel. As the modulation complexity is reduced, the throughput is generally equally reduced. Similarly, as the amount of coding is increased to provide more error correction, the overhead may consume more of the capacity of the channel, leaving less capacity for actual information. This may also reduce the throughput of the channel.